The mobile radio antennas provided for a base station normally have an antenna arrangement with a reflector in front of which a large number of antenna elements are provided, offset with respect to one another in the vertical direction. These antenna elements may, for example, transmit and receive in one polarization or in two mutually perpendicular polarizations. The antenna elements may be designed to receive in only one frequency band. The antenna arrangement may, however, also be in the form of a multiband antenna, for example for transmitting and receiving in two frequency bands with an offset with respect to one another. In principle, so-called triband antennas are also known.
As is known, mobile radio networks have a cellular form, with each cell having a corresponding associated base station with at least one mobile radio antenna for transmitting and receiving. The antennas are in this case designed such that they generally transmit and receive at a specific angle to the horizontal with a component pointing downwards, thus defining a specific cell size. This depression angle is also referred to, as is known, as the down-tilt angle.
In this context, a phase shifter arrangement has already been proposed in WO 01/13459 A1, in which the down-tilt angle can be adjusted in a continuously variable manner for a single-column antenna array with two or more antenna elements arranged one above the other. According to this prior publication, differential phase shifters are used for this purpose, and, when set differently, result in the delay time length and hence the phase shift at the two outputs of each phase shifter being set to a different direction, thus allowing the depression angle to be adjusted.
In this case, the setting and adjustment of the phase shifter angle is carried out manually or by means of a remotely controllable retrofitted unit, as is known by way of example from DE 101 04 564 C1.
When the so-called traffic density varies or, for example, a further base station adjacent to one cell is added to the antenna, then retrospective matching to changes in the characteristics can be carried out by preferably remotely controllable depression of a down-tilt angle, and by reducing the size of the cell.
However, such a change to a down-tilt angle is not the only or adequate solution for all situations.
Thus, for example, there are mobile radio antennas which have a fixed horizontal polar diagram, for example with a 3 dB beamwidth of 45°, 65°, 90° etc. In this case, matching to location-specific characteristics is impossible since it is not possible to change the polar diagram in the horizontal direction retrospectively.
However, in principle, mobile radio base station antennas also exist with polar diagrams which can be varied by means of intelligent algorithms in the base station. This necessitates, for example, the use of a so-called Butler matrix (via which, for example, an antenna array can be operated with two or more individual antenna elements which, for example, are arranged with a vertical offset one above the other in four columns). Antenna arrangements such as these are, however, enormously complex in terms of the antenna supply lines between the base station on the one hand and the antenna or the antenna elements on the other hand, with a dedicated feed cable being required for each column, and with two high-quality antenna cables being required for each column for so-called dual-polarized antennas, which are polarized at +45° and −45°, with an X-shaped alignment. This leads to a high cost price and to expensive installation. Finally, the base station also needs to have very complex algorithm circuits, thus once again increasing the overall costs.
An antenna arrangement with capabilities for power splitting and for setting different phase angles for the signals which can be supplied to the individual antenna elements has in principle also been disclosed in WO 02/05383 A1. The antenna comprises a two-dimensional antenna array with antenna elements and with a feed network. The feed network has a down-tilt phase adjusting device and an azimuth phase adjusting device with a device for setting the antenna element width (the width of the lobe). The beam width is varied by appropriately splitting the power differently between the antenna elements, which are offset with respect to one another in the horizontal direction. Phase shifter devices are provided in order to set a different azimuth beam direction, in order to set the emission direction appropriately.
The present illustrative exemplary non-limiting implementation provides an antenna arrangement and a method for its operation, which allows shaping of the polar diagram, particularly in the horizontal direction, and especially also in the form of a polar diagram change which can also be carried out retrospectively. This is preferably intended to be possible with little complexity for the feed cables that are required.
The solution according to the illustrative exemplary non-limiting implementation is thus based on the idea that the antenna has at least two antenna systems, each having at least one antenna element, that is to say, for example, at least in each case one antenna element, with the entire transmission energy now being supplied either to only one of the two antenna systems or else now being adjustable to achieve a different division of the power, as far as a 50:50 split of the power energy between the two antenna systems. Depending on the different components of the power that is supplied, this makes it possible to vary the polar diagram shape, particularly in the horizontal direction, and to vary the 3 dB beamwidth of an antenna from, for example 30° to 100°. In addition, the phase shifters which are provided allow the phase angle of the signals to be varied, in order to achieve a specific polar diagram shape.
If, for example, the at least two antenna elements are arranged in a preferred manner with the horizontal offset alongside one another on a common reflector, that is to say they transmit and receive in a common polarization plane, then this allows the horizontal polar diagram of the antenna to be adjusted. If, by way of example, the signals are supplied to an antenna array having at least two columns and having two or more antenna elements which are each arranged one above the other, then different horizontal polar diagrams can be produced for this antenna array, depending on the intensity and phase splitting.
The technology herein makes it possible, for example, to produce asymmetric horizontal polar diagrams, to be precise even when considered in the far field. It is also possible to produce horizontal polar diagrams for which, although they are symmetrical, that is to say they are arranged symmetrically with respect to a plane that runs vertically with respect to the reflector plane, the transmission signals are emitted with only a comparatively low power level in this vertical plane of symmetry. It is thus also possible to produce, for example, two, four etc. main lobes that are symmetrical with respect to this plane but which transmit more to the left and more to the right with an angled alignment position and, in between them preferably in the plane which is vertical with respect to the reflector plane, and which would intrinsically correspond to the main emission plane in the normal case, with the antenna arrangement transmitting with a considerably lower power level.
However, it is equally possible to produce horizontal polar diagrams which, for example, have an odd number of main lobes and in this case, if required, are arranged symmetrically with respect to a plane which runs at right angles to the reflector plane. In this case, one main lobe direction may preferably be located in the vertical plane of symmetry, or in a plane at right angles to the reflector plane. At least one further main lobe is in each case located on the left-hand side and on the right-hand side of the plane that is at right angles to the reflector plane. The intensity minima which are located between them may, for example, be reduced only by less than 10 dB, in particular by 6 dB or less than 3 dB. The antenna arrangement according to the illustrative exemplary non-limiting implementation and its operation thus make it possible to illuminate specific zones with a higher transmission intensity, depending on the special features on site, and in the process effectively to “mask out” other areas, or to supply them with only reduced radiation intensity. This offers advantages particularly when the horizontal polar diagram is adapted in areas in which there are schools, kindergartens etc., such that these areas are illuminated only very much more weakly.
In one illustrative exemplary non-limiting implementation, provision is even made for a different polar diagram shape to be produced for an antenna on the one hand for transmission and, in contrast to this, for reception. In other words, the horizontal polar diagrams for transmission and reception have different shapes. It is thus possible by means of a horizontal polar diagram which is optimally matched to the environment according to the illustrative exemplary non-limiting implementation to be used to take into account the fact, for transmission, that sensitive facilities such as kindergartens, schools, hospitals, etc. in the transmission zone are located in an area or zone which is supplied with only reduced intensity by a mobile radio antenna while, in contrast, the horizontal polar diagram for reception is designed such that the arriving signals can be received with correspondingly optimally designed horizontal polar diagrams throughout the entire coverage area of a corresponding mobile radio antenna in a cell.
The intensity and phase splitting according to the illustrative exemplary non-limiting implementation are preferably achieved by using a phase shifter arrangement, that is to say at least one phase shifter and preferably a differential phase shifter, and downstream hybrid circuit, in particular a 90° hybrid. This results, for example, in a signal which is supplied to a phase shifter and has a predetermined intensity being split between the two outputs of the differential phase shifter such that the intensities of the signals at the two outputs are the same, but their phases are different. If these two signals are supplied to the two inputs of a downstream 90° hybrid, then this now results in the phases once again being the same at the output of the hybrid, although the intensities or amplitudes of the signals are different. The amount of power which is supplied to the at least two phase shifters can in this way be split from, for example 1:0 to 1:1 by different phase settings on the phase shifter. The phase angle can also be influenced and the direction of the polar diagram varied by a further optional phase shifter which can be connected downstream.
In summary, the following advantages, by way of example, may be achieved by the system according to the illustrative exemplary non-limiting implementation:                Allowing location-specific antenna polar diagrams to be produced on site.        If required, the antenna polar diagram can be varied again and again at any time, for example when a new network plan is provided, without any need to replace the antenna itself.        During commissioning, the antenna polar diagram can be adapted easily, for example by remote control in the base station. No manual changes to the antenna on the pylon, such as alignment of the antenna etc., are required for this purpose, thus drastically reducing the costs.        Preset polar diagrams can easily be produced by means of fixed parameters, which can be preset, in the controller.        It is also possible to use an automatic control system to produce different polar diagrams at different times (for example as a function of given differences in the supply for the respective location as a function of other times of day, for example in the morning and in the evening, etc.).        The base stations can still be used even if the system according to the illustrative exemplary non-limiting implementation is upgraded. All that is required is simple replacement of the antenna on the base station.        Different polar diagrams can be produced for transmission and reception.        In particular, it is possible to supply sensitive areas with less power and other areas with more power.        Asymmetric horizontal polar diagrams can be produced.        Symmetrical horizontal polar diagrams can be produced, which have a number of superimposed main lobes such that the power in the first, second and for example, third lobes in three different azimuth directions in the horizontal polar diagram differ in terms of their power levels by less than 50%, in particular less than 40%, 30% or else less than 20% or even 10%.        